According to Madame Weatherby, what is the difference between a witch and a fairy in the novel, A Tale of Magic?

Madame Weatherberry makes the distinction between a witch and a fairy, which symbolizes her effort to make people understand that not all magic is bad. Though her argument turns out to be a lie, she does make the point that not everyone who can perform magic is evil. Her argument is that people with powers are either born as witches, and therefore practice evil witchcraft, or they are born as fairies and practice white magic that helps and heals.